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/*
* Copyright (c) 2022 SAP SE. All rights reserved.
* Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*
*/
#ifndef SHARE_SERVICES_NMT_PREINIT_HPP
#define SHARE_SERVICES_NMT_PREINIT_HPP
#include "memory/allStatic.hpp"
#ifdef ASSERT
#include "runtime/atomic.hpp"
#endif
#include "services/memTracker.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/macros.hpp"
class outputStream;
// NMTPreInit is the solution to a specific problem:
//
// NMT tracks C-heap allocations (os::malloc and friends). Those can happen at all VM life stages,
// including very early during the dynamic C++ initialization of the hotspot, and in CreateJavaVM
// before argument parsing.
//
// However, before the VM parses NMT arguments, we do not know whether NMT is enabled or not. Can we
// just ignore early allocations? If the only problem were statistical correctness, sure: footprint-wise
// they are not really relevant.
//
// But there is one big problem: NMT uses malloc headers to keep meta information of malloced blocks.
// We have to consider those in os::free() when calling free(3).
//
// So:
// 1) NMT off:
// a) pre-NMT-init allocations have no header
// b) post-NMT-init allocations have no header
// 2) NMT on:
// a) pre-NMT-init allocations have no header
// b) post-NMT-init allocations do have a header
//
// The problem is that inside os::free(p), we only get an opaque void* p; we do not know if p had been
// allocated in (a) or (b) phase. Therefore, we do not know if p is preceded by an NMT header which we
// would need to subtract from the pointer before calling free(3). There is no safe way to "guess" here
// without risking C-heap corruption.
//
// To solve this, we need a way to quickly determine, at os::free(p), whether p was a pre-NMT-init
// allocation. There are several ways to do this, see discussion under JDK-8256844.
//
// One of the easiest and most elegant ways is to store early allocation pointers in a lookup table.
// This is what NMTPreInit does.
//
//////////////////////////////////////////////////////////////////////////
//
// VM initialization wrt NMT:
//
//---------------------------------------------------------------
//-> launcher dlopen's libjvm ^
// -> dynamic C++ initialization |
// of libjvm |
// |
//-> launcher starts new thread (maybe) NMT pre-init phase : store allocated pointers in lookup table
// |
//-> launcher invokes CreateJavaVM |
// -> VM initialization before arg parsing |
// -> VM argument parsing v
// -> NMT initialization -------------------------------------
// ^
// ... |
// -> VM life... NMT post-init phase : lookup table is read-only; use it in os::free() and os::realloc().
// ... |
// v
//----------------------------------------------------------------
//
//////////////////////////////////////////////////////////////////////////
//
// Notes:
// - The VM will malloc() and realloc() several thousand times before NMT initialization.
// Starting with a lot of arguments increases this number since argument parsing strdups
// around a lot.
// - However, *surviving* allocations (allocations not freed immediately) are much rarer:
// typically only about 300-500. Again, mainly depending on the number of VM args.
// - There are a few cases of pre-to-post-init reallocs where pre-init allocations get
// reallocated after NMT initialization. Those we need to handle with special care (see
// NMTPreInit::handle_realloc()). Because of them we need to store allocation size with
// every pre-init allocation.
// For the lookup table, design considerations are:
// - lookup speed is paramount since lookup is done for every os::free() call.
// - insert/delete speed only matters for VM startup - after NMT initialization the lookup
// table is readonly
// - memory consumption of the lookup table matters since we always pay for it, NMT on or off.
// - Obviously, nothing here can use *os::malloc*. Any dynamic allocations - if they cannot
// be avoided - should use raw malloc(3).
//
// We use a basic open hashmap, dimensioned generously - hash collisions should be very rare.
// The table is customized for holding malloced pointers. One main point of this map is that we do
// not allocate memory for the nodes themselves. Instead we piggy-back on the user allocation:
// the hashmap entry structure precedes, as a header, the malloced block. That way we avoid extra
// allocations just to hold the map nodes. This keeps runtime/memory overhead as small as possible.
struct NMTPreInitAllocation {
NMTPreInitAllocation* next;
const size_t size; // (inner) payload size without header
// <-- USER ALLOCATION (PAYLOAD) STARTS HERE -->
NMTPreInitAllocation(size_t size) : next(NULL), size(size) {};
// Returns start of the user data area
void* payload() { return this + 1; }
const void* payload() const { return this + 1; }
// These functions do raw-malloc/realloc/free a C-heap block of given payload size,
// preceded with a NMTPreInitAllocation header.
static NMTPreInitAllocation* do_alloc(size_t payload_size);
static NMTPreInitAllocation* do_reallocate(NMTPreInitAllocation* old, size_t new_payload_size);
static void do_free(NMTPreInitAllocation* p);
};
class NMTPreInitAllocationTable {
// Table_size: keep table size a prime and the hash function simple; this
// seems to give a good distribution for malloced pointers on all our libc variants.
// 8000ish is really plenty: normal VM runs have ~500 pre-init allocations to hold,
// VMs with insanely long command lines maybe ~700-1000. Which gives us an expected
// load factor of ~.1. Hash collisions should be very rare.
// ~8000 entries cost us ~64K for this table (64-bit), which is acceptable.
static const int table_size = 7919;
NMTPreInitAllocation* _entries[table_size];
typedef int index_t;
const index_t invalid_index = -1;
static unsigned calculate_hash(const void* p) {
uintptr_t tmp = p2i(p);
unsigned hash = (unsigned)tmp
LP64_ONLY( ^ (unsigned)(tmp >> 32));
return hash;
}
static index_t index_for_key(const void* p) {
const unsigned hash = calculate_hash(p);
return hash % table_size;
}
const NMTPreInitAllocation* const * find_entry(const void* p) const {
return const_cast<NMTPreInitAllocationTable*>(this)->find_entry(p);
}
NMTPreInitAllocation** find_entry(const void* p) {
const unsigned index = index_for_key(p);
NMTPreInitAllocation** aa = (&(_entries[index]));
while ((*aa) != NULL && (*aa)->payload() != p) {
aa = &((*aa)->next);
}
assert((*aa) == NULL || p == (*aa)->payload(),
"retrieve mismatch " PTR_FORMAT " vs " PTR_FORMAT ".",
p2i(p), p2i((*aa)->payload()));
return aa;
}
public:
NMTPreInitAllocationTable();
// Adds an entry to the table
void add(NMTPreInitAllocation* a) {
void* payload = a->payload();
const unsigned index = index_for_key(payload);
assert(a->next == NULL, "entry already in table?");
a->next = _entries[index]; // add to front
_entries[index] = a; // of list
assert(find(payload) == a, "add: reverse lookup error?");
}
// Find - but does not remove - an entry in this map.
// Returns NULL if not found.
const NMTPreInitAllocation* find(const void* p) const {
return *(find_entry(p));
}
// Find and removes an entry from the table. Asserts if not found.
NMTPreInitAllocation* find_and_remove(void* p) {
NMTPreInitAllocation** aa = find_entry(p);
assert((*aa) != NULL, "Entry not found: " PTR_FORMAT, p2i(p));
NMTPreInitAllocation* a = (*aa);
(*aa) = (*aa)->next; // remove from its list
DEBUG_ONLY(a->next = NULL;) // mark as removed
return a;
}
void print_state(outputStream* st) const;
DEBUG_ONLY(void print_map(outputStream* st) const;)
DEBUG_ONLY(void verify() const;)
};
// NMTPreInit is the outside interface to all of NMT preinit handling.
class NMTPreInit : public AllStatic {
static NMTPreInitAllocationTable* _table;
// Some statistics
static unsigned _num_mallocs_pre; // Number of pre-init mallocs
static unsigned _num_reallocs_pre; // Number of pre-init reallocs
static unsigned _num_frees_pre; // Number of pre-init frees
static void create_table();
static void add_to_map(NMTPreInitAllocation* a) {
assert(!MemTracker::is_initialized(), "lookup map cannot be modified after NMT initialization");
// Only on add, we create the table on demand. Only needed on add, since everything should start
// with a call to os::malloc().
if (_table == NULL) {
create_table();
}
return _table->add(a);
}
static const NMTPreInitAllocation* find_in_map(void* p) {
assert(_table != NULL, "stray allocation?");
return _table->find(p);
}
static NMTPreInitAllocation* find_and_remove_in_map(void* p) {
assert(!MemTracker::is_initialized(), "lookup map cannot be modified after NMT initialization");
assert(_table != NULL, "stray allocation?");
return _table->find_and_remove(p);
}
// Just a wrapper for os::malloc to avoid including os.hpp here.
static void* do_os_malloc(size_t size);
public:
// Switches from NMT pre-init state to NMT post-init state;
// in post-init, no modifications to the lookup table are possible.
static void pre_to_post();
// Called from os::malloc.
// Returns true if allocation was handled here; in that case,
// *rc contains the return address.
static bool handle_malloc(void** rc, size_t size) {
size = MAX2((size_t)1, size); // malloc(0)
if (!MemTracker::is_initialized()) {
// pre-NMT-init:
// Allocate entry and add address to lookup table
NMTPreInitAllocation* a = NMTPreInitAllocation::do_alloc(size);
add_to_map(a);
(*rc) = a->payload();
_num_mallocs_pre++;
return true;
}
return false;
}
// Called from os::realloc.
// Returns true if reallocation was handled here; in that case,
// *rc contains the return address.
static bool handle_realloc(void** rc, void* old_p, size_t new_size) {
if (old_p == NULL) { // realloc(NULL, n)
return handle_malloc(rc, new_size);
}
new_size = MAX2((size_t)1, new_size); // realloc(.., 0)
if (!MemTracker::is_initialized()) {
// pre-NMT-init:
// - the address must already be in the lookup table
// - find the old entry, remove from table, reallocate, add to table
NMTPreInitAllocation* a = find_and_remove_in_map(old_p);
a = NMTPreInitAllocation::do_reallocate(a, new_size);
add_to_map(a);
(*rc) = a->payload();
_num_reallocs_pre++;
return true;
} else {
// post-NMT-init:
// If the old block was allocated during pre-NMT-init, we must relocate it: the
// new block must be allocated with "normal" os::malloc.
// We do this by:
// - look up (but not remove! lu table is read-only here.) the old entry
// - allocate new memory via os::malloc()
// - manually copy the old content over
// - return the new memory
// - The lu table is readonly so we keep the old address in the table. And we leave
// the old block allocated too, to prevent the libc from returning the same address
// and confusing us.
const NMTPreInitAllocation* a = find_in_map(old_p);
if (a != NULL) { // this was originally a pre-init allocation
void* p_new = do_os_malloc(new_size);
::memcpy(p_new, a->payload(), MIN2(a->size, new_size));
(*rc) = p_new;
return true;
}
}
return false;
}
// Called from os::free.
// Returns true if free was handled here.
static bool handle_free(void* p) {
if (p == NULL) { // free(NULL)
return true;
}
if (!MemTracker::is_initialized()) {
// pre-NMT-init:
// - the allocation must be in the hash map, since all allocations went through
// NMTPreInit::handle_malloc()
// - find the old entry, unhang from map, free it
NMTPreInitAllocation* a = find_and_remove_in_map(p);
NMTPreInitAllocation::do_free(a);
_num_frees_pre++;
return true;
} else {
// post-NMT-init:
// - look up (but not remove! lu table is read-only here.) the entry
// - if found, we do nothing: the lu table is readonly, so we keep the old address
// in the table. We leave the block allocated to prevent the libc from returning
// the same address and confusing us.
// - if not found, we let regular os::free() handle this pointer
if (find_in_map(p) != NULL) {
return true;
}
}
return false;
}
static void print_state(outputStream* st);
static void print_map(outputStream* st);
DEBUG_ONLY(static void verify();)
};
#endif // SHARE_SERVICES_NMT_PREINIT_HPP
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